AENDO October 40/4

Chandramouli, Visvanathan, Karin Ekberg, William C. Schumann, John Wahren, and Bernard R. Landau. Origins of the hydrogen bound to carbon 1 of glucose in fasting: significance in gluconeogenesis quantitation. Am. J. Physiol. 277 (Endocrinol. Metab. 40): E717–E723, 1999.— Healthy subjects ingested H2O. 2H enriched the hydrogen bound to carbon 1 of blood glucose 1.3 to 1.8 times more than the hydrogens bound to carbon 6. Enrichment at carbon 1 was more than at carbon 5 after 14 h, but not after 42 h, of fasting. After overnight fasting, when [2,3-3H]succinate was infused, 34 times as much 3H was bound to carbon 6 as to carbon 1. On [1-2H,1-3H,1-14C]galactose infusion, the ratios of 2H to 14C and of 3H to 14C in blood glucose were 30% less than in the galactose. 3H at carbon 6 was 1% of that at carbon 1 of the glucose. Thus, although the two hydrogens bound to carbon 1 and the two bound to carbon 6 of fructose 6-phosphate (p) during gluconeogenesis are equally enriched in 2H via pyruvate’s equilibration with alanine, one of each is further enriched via hydration of fumarate that is converted to glucose. That hydrogen at carbon 1 of fructose 6-phosphate (P) is also enriched in fructose 6-P’s equilibration with mannose 6-P. 2H from H2O at carbon 1 to carbon 2 of blood glucose cannot then quantitate gluconeogenesis because of [1-2H]glucose formation during glycogenolysis. Triose-P cycling has a minimal effect on quantitation. 2H recovery in glucose from [1-2H]galactose does not quantitate galactose conversion via UDP-glucose to glycogen.